Crosslinked olefinic foams are typically made from ethylenic polymers such as low density polyethylene, ethylene vinylacetate copolymer, homogeneous ethylene and/or .alpha.-olefin homopolymers or interpolymers comprising ethylene and/or C.sub.3 -C.sub.20 .alpha.-olefins including the substantially linear ethylene/.alpha.-olefin interpolymers. These include the polyolefin plastomers, such as those marketed by The Dow Chemical Company under the AFFINITY.TM. tradename and polyethylene elastomers, such as those marketed under the ENGAGE.TM. tradename by Du Pont Dow Elastomers PLC.
Crosslinking is achieved by conventional means such as peroxides, silane and/or radiation. Some of the advantages of crosslinked foam over noncrosslinked foams are smaller cell sizes (typically less than about 1 mm), smooth skin and thermoformability. However, there are several disadvantages of crosslinked foams, such as: (1) the chemical blowing agents used (for example, azodicarbonamide) are expensive; (2) crosslinked foams expanded with nitrogen are made in energy intensive equipment at high pressures (typically about 10,000 to 30,000 psi); (3) the processes used to make the foams are typically batch processes which are expensive to operate; and (4) the foams cannot be recycled. On the other hand, non-crosslinked olefinic foams are made in continuous processes at relatively high production rates using less expensive physical blowing agents (such as isobutane) and the foams can be recycled (which is environmentally desirable), but these foams are difficult to thermoform.
It is desirable to make soft and flexible non-crosslinked foams with small cell sizes and good aesthetics that could be used as alternatives to crosslinked foams without the disadvantages listed above. We have surprisingly found that non-crosslinked foams made from blends of alkenyl aromatic polymers and specific types and amounts of substantially random interpolymers are soft and flexible with small cell sizes. Furthermore, the foams are thermoformable and can be recycled.